Appendix E
Data Source and Accuracy Statements
Chapter 4 Energy and the Environment
PETROLEUM SUPPLY
TABLE 4-1. Overview of U.S. Petroleum Production,
Imports, Exports, and Consumption
The petroleum supply system is extremely complicated, with many different processes,
products, and entities involved. Briefly, crude oil is produced or imported,
transported to refineries where it is refined into various products, and then
transported to markets. Imports and exports of crude oil and products must be
accounted for, as must be nonpetroleum components of final products, such as
natural gas plant liquids and ethanol for gasoline blending.
The U.S. Department of Energy, Energy Information Administration (EIA) collects
extensive data at select points in the petroleum supply system. Sixteen surveys
are conducted by EIA's Petroleum Supply Reporting System to track the supply
and disposition of crude oil, petroleum products, and natural gas plant liquids:
- five weekly surveys cover refineries (form EIA-800), bulk terminal stocks
(form EIA-801), product pipelines (form EIA-802), crude stocks (form EIA-803),
and imports (form EIA-804).
- eight monthly surveys cover the same five points plus tanker and barge movement
(form EIA-817), gas processing facilities (form EIA-816), and oxygenates (form
EIA-819M).
- one survey (form EIA-807) collects propane data on a monthly basis in the
warmer months (April-September) and on a weekly basis in the colder months.
- one annual survey determines production capacity of oxygenates and fuel
ethanol (form EIA-819A), and
- one annual survey determines refinery fuel use, capacity, and crude oil
receipts by transportation mode (form EIA-820).
The five weekly surveys target key points in the petroleum supply system. They
do not include all companies, but sample 90 percent of volume at each selected
point in the supply system. EIA rank-orders the companies involved in the survey
and sends surveys as it scrolls down the list, stopping when it reaches the
90 percent level. Although 100 percent coverage is sacrificed, this method keeps
the level of incoming data manageable and avoids burdening the smallest companies.
All data are reviewed and anomalies checked.
Monthly surveys provide data that are used in the monthly and annual reports.
They are similar to the weekly surveys, but are more exhaustive in both the
range of data collected and the depth of the collection. Sample sizes and response
rates for several of the key points in the supply system are shown in table
1.The eight monthly surveys cover the industry more accurately than the weekly
surveys and provide some double-check points that the other surveys do not.
EIA expends considerable effort to ensure that its data are as accurate as possible.
Revisions are made throughout the year. For example, EIA's Annual Energy
Review 1996, released in July 1997, provided a preliminary 1996 number for
total petroleum production of 8.30 million barrels per day (mmbd). The Annual
Energy Review 1997, released a year later, revised that to 8.25 mmbd, and
the 1999 Review reported 8.29 mmbd.
No complicated survey is likely to be 100 percent accurate. EIA lists four
sources of potential systematic errors:
- Some members of the target population are missed. EIA reports that it continually
reviews the lists and searches industry periodicals and newspapers to identify
new actors. Considering the nature of the petroleum industry, it is very unlikely
that companies with significant production are not surveyed.
- Some members of the target population do not respond. EIA reports a 97 percent
response rate for monthly surveys. For some points in the supply system, the
average response is over 99 percent. Survey respondents are required by law
to respond, but some nonresponse is inevitable, especially among small companies.
EIA assumes that the nonrespondent's value for that month is the same as for
the previous month except for imports. Since imports vary widely, with respondents
frequently having no imports, EIA assumes a nonresponse means zero imports.
It can be assumed that EIA is good at "filling in the blanks." Assuming for
illustration purposes that 0.5 percent of production does not respond, and
that EIA is 90 percent accurate in covering the gap, then there is a possibility
of a 0.05 percent error. Applying that to total production of 8.29 mmbd in
1999 suggests that there could be an error of 0.0041 mmbd (4,100 barrels per
day), which would not affect the published number.
- The most serious problem may be response error. A company may have poor
data, perhaps as a result of imperfect measurements, or it may transmit the
wrong number. EIA has no control over a company's data quality. Companies
have incentive to measure their inputs and products accurately. Otherwise,
they may be cheating themselves or risking ill will with their customers or
suppliers. However, no instrumentation is perfectly accurate. The high throughput
of, say, a refinery with capacity of several hundred thousand barrels per
day, with a variety of products changing density and some lost or used on
site, is very complicated to measure. Instrumentation errors are likely to
be systematic at any one site, although they will be more nearly random in
the aggregate for all facilities. There is potential for small but significant
overall errors.
Mistakes may be made in recording and transferring the data. EIA reviews the
data and flags gross errors or missing data for review by the respondent.
However, not all errors will be picked up by EIA and/or the respondent. Overall,
response errors probably are several times as large as nonresponse errors,
but it is beyond the scope of this profile to estimate them.
- The final potential source of systematic error is in the clarity of the
survey form, i.e., whether all respondents interpret it correctly. No doubt
errors and ambiguities can creep into a form, but at least for petroleum supply,
that does not appear to be a major risk. The supply system is not changing
rapidly, and EIA should be able to keep with it and the terminology. However
the final digit of EIA's published supply data is questionable.
For additional information on survey methodology and statistical reliability,
the reader is referred to the EIA reference cited in the tables or the EIA Internet
site at www.eia.doe.gov.
FUEL AND ENERGY CONSUMPTION
TABLE 4-1. Overview of U.S. Petroleum Production,
Imports, Exports, and Consumption
TABLE 4-2. U.S. Consumption of Energy from Primary
Sources by Sector
TABLE 4-3. Domestic Demand for Refined Petroleum
Products by Sector
TABLE 4-4. U.S. Energy Consumption by the Transportation
Sector
TABLE 4-7. Domestic Demand for Gasoline
Petroleum consumption is far more complex to measure than supply. Instead of
a few hundred companies at most measuring points in the supply system, there
are tens of millions of consumers. It would be impossible for any survey of
individual consumers to produce the high rate of return of U.S. Department of
Energy (DOE), Energy Information Administration's (EIA's) supply surveys. EIA's
transportation data collection is further limited by the termination of the
Residential Transportation Energy Consumption Survey (RTECS). Therefore, EIA
uses surveys of sales of products (e.g., Form EIA-821:Annual Fuel Oil and Kerosene
Sales Report) or tax collection data from the U.S. Department of Transportation,
Federal Highway Administration (FHWA).
EIA reviewed the accuracy of its energy consumption data in a 1990 monograph
Energy Consumption by End-Use Sector, a Comparison of Measures by Consumption
and Supply Surveys. Unfortunately, this monograph does not discuss the transportation
sector because the consumption and supply surveys were not comparable. However,
some of the results from other sectors indicate the discrepancies between supply
and consumption surveys. Table 4-2 shows the ratio of fuel supplied to the sector
to consumption reported by the sector in consumption surveys.
In most cases, supply is reported as substantially larger than consumption.
Supplies of fuel oil to the commercial sector are reported at almost twice the
level of consumption reported by that sector. Some of the discrepancies may
be due to definition differences (e.g., fuel oil for apartment buildings is
included in commercial supply surveys but not in consumption surveys.) Overall,
however, the differences are too large for great confidence in the accuracy
of the data.
If transportation had been reviewed in the same format, it is likely that the
discrepancies would have been larger. Most transportation fuel (gasoline for
automobiles) is purchased in small quantities at irregular intervals and cannot
be checked simply by looking at a utility bill. Hence, highway transportation
energy consumption surveys must be extensive to avoid the risk of large uncertainties
in the data. But, with the termination of the RTECS, EIA ceased conducting such
surveys. Consumption data must be derived indirectly from sales of petroleum
products and tax collection data. While petroleum supply may be accurate to
one decimal place, it is likely that disaggregating by sector use may be within
plus or minus several percentage points, or perhaps about half a quadrillion
British thermal unit (Btu) in table 4-1.
Motor Gasoline
Almost all gasoline is consumed in the transportation sector. Small amounts
are used in the commercial sector for nonhighway use and the industrial sector,
which includes agriculture, construction, and other uses. Subtracting estimates
of those uses from the known total sales yields the transportation sector's
total, which is further subdivided into highway and marine use. Aviation gasoline
is, of course, used entirely in the transportation sector (for a very few high-performance
automobiles as well as small aircraft).
Data on actual sales is collected by the states for revenue purposes. These
data are forwarded to FHWA. EIA uses the data from FHWA to allocate highway
consumption of motor gasoline among the states. For 1999, FHWA reported 124.7
billion gallons of gasoline sold nationally for highway use. EIA's table 5.12c
of the Annual Energy Review 2000 lists 8.33 mmbd of gasoline supplied
for the transportation sector, the same as 127.7 billion gallons.
Such close agreement between supply and demand is not totally convincing. Definitions
are unique to each state (e.g., whether gasohol is counted as pure gasoline
or part gasoline and part renewables), measurement points vary from state to
state, and each state handles losses differently. Hence, the total of all states'
sales of gasoline is not entirely consistent.
Separation of highway from nonhighway uses of gasoline is, by necessity, based
in part on careful estimates. Nevertheless, overall gasoline sales are well
documented, and the separation is probably fairly accurate. Refinery output
of motor gasoline was 7.93 mmbd in 1999, which is probably accurate to the first
decimal place and maybe a little better. The transportation sector's 8.33 mmbd
would have about the same accuracy.
Diesel Fuel
Diesel fuel is used in highway vehicles, railroads, boats, and military vehicles.
Sales are only about 30 percent of gasoline in the transportation sector, but
uncertainties are greater. More diesel than gasoline is used for nonhighway
purposes, especially agriculture and construction. In addition, there has been
more potential for cheating to avoid the tax; heating oil is virtually the same
as diesel fuel and can easily be transferred to a vehicle. However, this is
less significant now that tracers have been added to fuel oil. After the addition
of tracers, the amount of transportation diesel fuel use jumped.
To estimate diesel fuel sales by mode, EIA starts with the total supply of
distillate fuel and subtracts the small amount sold to electric utilities (the
most accurately known sector, as measured by EIA Form EIA-759). The remainder
is divided among the other end-use sectors according to EIA's sales surveys
(Form EIA-821: Annual Fuel Oil and Kerosene Sales Report, and Form EIA-863:
Petroleum Product Sales Identification Survey).
This method introduces several potential elements of inaccuracy. First, the
surveys of each sector are probably less accurate than the supply surveys noted
earlier. Companies and individuals may inadvertently send incorrect data, or
not respond at all. Then EIA has to determine what adjustment factor to use
for each end-use sector. Since each sector will have a different response rate
to the surveys, the adjustments will be different. Large adjustments can introduce
large errors. EIA has not published its adjustments for the transportation sector.
As shown in table 2, the adjustments in other sectors range from 5 to 96 percent
of reported consumption. Even a 20 percent adjustment could introduce an error
of one or two percentage points (plus or minus) for any one sector.
Overall, the accuracy of diesel fuel use in the transportation sector should
be viewed with some skepticism.
Jet Fuel
Jet fuel is the only other petroleum-based fuel that is used in large quantities
(over 1 million barrels/day) in the transportation sector. Virtually all of
it is used by airlines. These data are accurate because airlines are required
to report usage, and because there are relatively few certificated air carriers,
data collection should be manageable.
NONPETROLEUM FUELS CONSUMPTION
TABLE 4-10. Estimated Consumption of Alternative
and Replacement Fuels for Highway Vehicles
Collectively, oxygenates, natural gas, electricity, and various alternative
fuels amount to only about 3 percent of all energy used in the transportation
sector. While this may not be much greater than the error bars associated with
petroleum use, it is important to track changes in these fuels accurately.
Oxygenates
Oxygenates, mostly methyl tributyl ether (MTBE), which is derived from natural
gas and ethanol, are part of mainstream gasoline supply. They are measured routinely
with petroleum supply (forms EIA-819A and 819M). Consumption is estimated from
production, net imports, and stock changes. Refineries and other entities are
required to report data on oxygenates, and EIA also monitors production capability
to provide a crosscheck. Thus, oxygenates data are likely to be reasonably accurate.
Natural Gas
Natural gas is used in the transportation sector mainly as the fuel for compressor
stations on natural gas transmission lines. A small but growing amount is used
in compressed or liquefied form in vehicles. EIA collects data on natural gas
much as it does for petroleum, but the system is much simpler. Natural gas transmission
companies may not know exactly how much gas is used in compressor stations,
but they have a good idea based on the size of the equipment and the load on
the line. The reported numbers probably are reasonably accurate. Data on natural
gas-fueled vehicles are collected by DOE via Form-886, which is sent to fuel
suppliers, vehicle manufacturers, and consumers. In addition, private associations
and newsletters are important sources of information on alternative vehicles
and alternative fuels use. Since most groups work cooperatively with DOE, it
is likely that the data reported are accurate. EIA tracks the number of natural
gas vehicles and the number of refueling stations to provide a cross check on
estimates of natural gas consumption.
Electricity
Electricity powers intercity trains (Amtrak) and intracity rail systems. In
addition, the number of electric vehicles is growing. There is considerable
uncertainty over the energy consumed by these modes. Amtrak no longer provides
national totals of its electricity consumption. Data on intracity transit is
based on U.S. Department of Transportation, Federal Transit Administration's
(FTA's) National Transit Database (NTD). The legislative requirement for the
NTD is found in Title 49 U.S.C. 5335(a). Transit agencies receiving funds through
the Urbanized Area Formula Program are generally required to report financial
and operating data, including energy use. Although the data is generally considered
accurate because FTA reviews and validates information submitted, reliability
may vary because some transit agencies cannot obtain accurate information or
may misinterpret certain data.
If electric vehicles become important over the next decade or two, dedicated
charging stations may become commonplace, which could provide accurate data.
Fleet owners (e.g., electric utilities) can keep accurate records, but individuals
who plug their vehicles in at home may not. Electricity use must be estimated
from the number of such vehicles and the expected driving cycles. Hence, data
on electric power for transportation must be viewed as an estimate.
It should also be noted that electricity is a form of work that usually is
generated from heat with the loss of about two-thirds of the energy. Automobile
engines are equivalent to electric generators in that they convert chemical
energy to heat and then to work, losing most of the energy as waste heat. When
electrical energy is compared to petroleum in transportation, the waste heat
must be included for consistency. A kilowatt-hour of electricity is equivalent
to 3,413 British thermal units (Btu), but about 10,000 Btu of heat are required
to produce it. This factor is dropping as generators become more efficient.
High efficiency gas turbines may require 8,000 Btu or less, but the average
is much higher. It is usually impossible to tell where the power for a specific
use is generated, so average figures for a region are used to estimate the waste
energy, a factor that further reduces the accuracy of the data.
Alternative Fuels
In addition to oxygenates, natural gas, and electricity, alternative fuels
include ethanol and methanol. EIA tracks the numbers of such vehicles through
Form-886, state energy offices, federal demonstration programs, manufacturers,
and private associations. These numbers probably are fairly accurate although
it is difficult to monitor retirements. Fuel consumption is estimated from the
types of vehicles in operation, vehicle miles traveled, and expected fuel efficiency.
Adjustments are necessary for the relatively few flexible-fuel vehicles. Obviously,
the reported data are estimates only.
FUEL AND ENERGY CONSUMPTION BY MODE
TABLE 4-5. Fuel Consumption by Mode of Transportation
TABLE 4-6. Energy Consumption by Mode of Transportation
TABLE 4-8. Certificated Air Carrier Fuel Consumption
and Travel
TABLE 4-9. Motor Vehicle Fuel Consumption and
Travel
TABLE 4-11. Passenger Car and Motorcycle Fuel
Consumption and Travel
TABLE 4-12. Other 2-Axle 4-Tire Vehicle Fuel Consumption
and Travel
TABLE 4-13. Single-Unit 2-Axle 6-Tire or More
Truck Fuel Consumption and Travel
TABLE 4-14. Combination Truck Fuel Consumption
and Travel
TABLE 4-15. Bus Fuel Consumption and Travel
Fuel consumption data are collected quite differently than supply data collected
by the U.S. Department of Energy, Energy Information Administration (EIA). Highway
fuel consumption, for example, is based on U.S. Department of Transportation,
Federal Highway Administration (FHWA) data collected from states in the course
of revenue collection. EIA starts from the fuel delivered to transportation
entities.
Highway
Highway fuel data (tables 4-5, 4-9, and 4-11 through 4-15) are collected mainly
by FHWA. All states plus the District of Columbia report total fuel sold along
with travel by highway category and vehicle registration. Data typically flows
from state revenue offices to the state departments of transportation to FHWA.
Even if reporting is reasonably accurate, some data are always anomalous or
missing and must be modified to fit expected patterns. In addition, as discussed
earlier, there are some significant differences in methodology and definitions
among the states. In particular, states differ in where the tax is applied in
the fuel supply system, how gasohol is counted, how nonhighway use is treated,
and how losses are handled.
Nonhighway use of gasoline and diesel fuel is a particularly large source of
potential error. Some states designate nonhighway users as tax-exempt, others
make the tax refundable. In either case, many people won't bother to apply if
the amount of money is small. Nonhighway use of diesel fuel is especially large
because many construction and agricultural vehicles are diesel powered. Thus,
the fraction of petroleum attributed to transportation could be overestimated.
On the other hand, some nonhighway fuel finds its way into the transportation
system because heating oil can be used as diesel fuel, evading the tax. Tracers
are now added to heating oil, which appears to have reduced the level of such
tax evasion-if found in a truck's fuel tank, the tracer indicates diversion
from a nontaxed source.
Breaking fuel use down by class of motor vehicle introduces the potential for
error. FHWA must estimate the miles each class is driven and the fuel economy.
Estimation of miles is based on the 1995 Nationwide Personal Transportation
Survey (NPTS), administered by FHWA, and the Vehicle Inventory and Use Survey
(formerly known as the Truck Inventory and Use Survey) conducted by the U.S.
Census Bureau. For information about these two surveys, the reader is referred
to the technical appendix of Our Nation's Travel, available from the
FHWA, Office of Highway Information Management; and the 1997 Census of Transportation,
available from the Economics and Statistics Administration within the Census
Bureau. Fuel economy is based on state-supplied data, TIUS, and the National
Highway Traffic Safety Administration data on new car fuel economy, which must
be reduced by about 15 percent to reflect actual experience on the road. Overall,
both vehicle-miles of travel and fuel economy are estimates.
Fuel consumption by buses is particularly uncertain. FHWA collects data on
intercity buses, and the American Public Transit Association (APTA) covers local
travel. Very little data are collected on school buses. APTA figures are based
on data from the USDOT, Federal Transit Administration's (FTA's) National Transit
Database, which covers about 90 to 95 percent of total passenger-miles. These
data are generally accurate because FTA reviews and validates information submitted
by individual transit agencies. Reliability may vary because some transit agencies
cannot obtain accurate information or may misinterpret data. APTA conservatively
adjusts the FTA data to include transit operators that do not report to FTA,
such as private and very small operators and rural operators. Prior to 1984,
APTA did not include most rural and demand responsive systems.
Air
The U.S. Department of Transportation, Bureau of Transportation Statistics,
Office of Airline Information (OAI) is the source of these data. The numbers
are based on 100-percent reporting of fuel use by large certificated air carriers
(those with revenues of more than $100 million annually) via Form 41.The data
are probably reasonably accurate because the airlines report fuel use regularly,
and the limited number of airlines aids data management.
Smaller airlines, such as medium size regional and commuter air carriers, are
not required to report energy data. OAI estimates that about 8 percent would
have to be added to the total of the larger airlines to account for this use,
but that has not been done in table 4-5 or 4-8.
General aviation aircraft and air taxis are covered in the General Aviation
and Air Taxi and Avionics Survey, conducted by the Federal Aviation Administration
(FAA). The survey is conducted annually and encompasses a stratified, systematic
design from a random start to generate a sample of all general aviation aircraft
in the United States. It is based on the FAA registry as the sampling frame.
For instance, in 2000, a sample of 31,039 aircraft was identified and surveyed
from an approximate population of 256,927 registered general aviation aircraft.
The reliability of the GAATA survey can be impacted by two factors: sampling
and nonsampling error. A measure, called the standard error, is used to indicate
the magnitude of sampling error. Standard errors can be converted for comparability
by dividing the standard error by the estimate (derived from the sample survey
results) and multiplying it by 100. This quantity, referred to as the percent
standard error, totaled two and four-tenths of a percent in 2000 for the general
aviation fleet. A large standard error relative to an estimate indicates lack
of precision, and inversely, a small standard error indicates precision.
Nonsampling errors could include nonresponse, a respondent's inability or unwillingness
to provide correct information, differences in interpretation of questions,
and data entry mistakes. The reliability of general aviation fleet data comparisons
over time would decrease because of changes implemented in 1978 and sampling
errors discussed above. Readers should note that nonresponse bias may be a component
of reliability errors in the data from 1980 to 1990. The FAA conducted telephone
surveys of nonrespondents in 1977, 1978, and 1979 and found no significant differences
or inconsistencies between respondent and nonrespondent replies. The FAA discontinued
the telephone survey of nonrespondents in 1980 to save costs. Nonresponse surveys
were resumed in 1990; and the FAA found notable differences and make adjustments
to its data to reflect nonresponse bias.
The U.S. Government, in particular the Department of Defense (DOD), uses a
large amount of jet fuel as shown in table4-19 (see discussion on government
consumption below). However, DOD reports all fuel purchased, including from
foreign sources for operations abroad. While the data may be accurate, it is
not comparable to EIA's overall U.S. supply and consumption figures on jet fuel.
International operations are included in table 4-8 but not table 4-5. The fuel
use for international operations includes that purchased by U.S. airlines for
return trips. OAI does not collect data on foreign airline purchases of fuel
in the United States. Thus, a significant use of U.S. jet fuel is missed. However,
these two factors approximately balance each other out. As shown in table 1-34,foreign
carrier traffic is just slightly less than U.S. carrier international traffic,
so presumably the fuel purchased here by foreign carriers is very close to the
fuel purchased abroad by U.S. carriers.
Rail
The data are from Railroad Facts, published annually by the Association
of American Railroads (AAR). AAR figures are based on 100 percent reporting
by Class I railroads to the Surface Transportation Board (STB) via Schedule
700 of the R1 Annual Report. Thus, the data are considered accurate.
STB defines Class I railroads as having operating revenues at or above a threshold
indexed to a base of $250 million (1991) and adjusted annually in concert with
changes in the Railroad Freight Rate Index published by the Bureau of Labor
Statistics. In 2001, the adjusted threshold for Class I railroads was $266.7
million. Although Class I railroads represent only 1 percent of the number of
railroads in the country, they account for over 70 percent of the industry's
mileage operated and more than 90 percent of all freight revenue; energy consumption
should be of the same order. For passenger travel, information is unavailable.
Amtrak no longer provides data on a national basis, and the regional data appears
to be inconsistent.
Transit
The APTA figures are based on information in FTA's National Transit Database.
APTA conservatively adjusts FTA data to include transit operators that do not
report to the FTA Database (private and very small operators and rural operators),
which accounts for about 90 to 95 percent of the total passenger-miles. The
data are generally accurate because the FTA reviews and validates information
submitted by individual transit agencies. Reliability may vary because some
transit agencies cannot obtain accurate information or misinterpret certain
data definitions in federal guidelines.
Water
The EIA collects data on residual and distillate fuel oils and diesel through
its Annual Fuel Oil and Kerosene Sales Report survey, form EIA-821.The
survey targets companies that sell fuel oil and kerosene to end users. This
survey commenced in 1984 and data from previous years should be used with caution.
Sampling Frame and Design
The sample's target universe includes all companies that sell fuel oil and
kerosene to end users. EIA derives the sampling frame from the EIA-863 database
containing identity information for approximately 22,300 fuel oil and kerosene
sellers. EIA stratifies the sampling frame into two categories: companies selected
with certainty and uncertainty. Those in the certainty category varied but included
the end use "vessel bunkering," or sales for the fueling of commercial and private
watercraft.
Sampling Error, Imputation, and Estimates
EIA reported a 92.5 percent response rate for the 2000 survey. The EIA also
provides estimates of the sampling error for geographic areas and U.S. averages
are 1.8 for residential distillate fuel oil, 0.8 for nonresidential retail distillate
fuel oil, and 0.1 for retail residual fuel oil. Some firms inevitably ignore
survey requests, causing data gaps. EIA estimates the volumes of these firm's
sales by imputation; more detailed information and the algorithm can be obtained
at EIA's web site in the technical notes for the Annual Fuel Oil and Kerosene
Sales Report. See http://www.eia.doe.gov/oil gas/petroleum/data publications/fuel oil and kerosene sales/foks.html.
TABLE 4-19. U.S. Government Energy Consumption
by Agency and Source
Energy consumption data are collected by DOE's Office of Federal Energy Management
Programs in cooperation with most departments and agencies. DOD is by far the
largest consumer, accounting for about 80 percent of the total. As discussed
above, the data includes fuel purchased abroad for military bases. Since government
agencies are required to report these data, they are probably accurate. However,
it is possible that some consumption is missed. For example, some agencies may
report only fuel supplied directly, missing consumption such as gasoline purchased
by employees while on government business for which they are then reimbursed.
In addition, smaller agencies were neglected. Overall, however, the data should
provide a fairly good approximation of government energy consumption.
ENERGY EFFICIENCY
TABLE 4-20. Energy Intensity of Passenger Modes
TABLE 4-21. Energy Intensity of Certificated Air
Carriers, All Services
TABLE 4-22. Energy Intensity of Passenger Cars,
Other 2-Axle 4-Tire Vehicles, and Motorcycles
TABLE 4-24. Energy Intensity of Transit Motor
Buses
TABLE 4-25. Energy Intensity of Class I Railroad
Freight Service
TABLE 4-26. Energy Intensity of Amtrak Service
Total energy consumed for each mode can be estimated with reasonable accuracy.
Miles traveled are known for some modes, such as air carriers, but less accurately
for others, most notably automobiles. When the numbers of passengers or tons
are required to calculate energy efficiency, another uncertainty is introduced.
Again, air carriers and intercity buses know how many passengers are on board
and how far they travel, but only estimates are available for automobiles and
intracity buses.
Thus, table 4-21 should be quite accurate for certificated air carriers, though
it is missing small airlines and private aircraft. Table 4-22 is based on FHWA
fuel tax data, derived from state fuel tax revenues. VMT is as discussed for
tables 1-9 and 1-10.Data for motorcycles must be adjusted significantly more
than for automobiles because less information is collected from the states or
from surveys. Transit bus data (table 4-24) are very uncertain because, unlike
intercity buses, the distance each passenger travels is not measured by ticket
sales.
The intermodal comparison of passenger travel in table 4-20 must be viewed
with considerable caution. Data for the different modes are collected in different
ways, and the preparation of the final results is based on different assumptions.
As noted above, airlines accurately record passenger miles, but the data on
occupancy of private automobiles must be estimated from surveys. Even relatively
certain data, such as state sales of gasoline, must be modified to resolve anomalies,
and transit data are even harder to make consistent. Furthermore, different
groups collect the data for the various modes, and they have different needs,
assumptions, and methodologies. Thus, the comparisons are only approximate.
Freight service data (table 4-25) are from Railroad Facts, published
annually by the Association of American Railroads (AAR).AAR figures are based
on 100 percent reporting by Class I railroads to the Surface Transportation
Board (STB) via Schedule 700 of the R1 Annual Report. STB defines Class
I railroads as having operating revenues at or above a threshold indexed to
a base of $250 million (1991) and adjusted annually in concert with changes
in the Railroad Freight Rate Index published by the Bureau of Labor Statistics.
In 2000, the adjusted threshold for Class I railroads was $ 261.9 million. Although
Class I railroads comprise only 1 percent of the number of railroads in the
country, they account for over 71 percent of the industry's mileage and 91 percent
of all freight revenue; energy data should be of the same order.
TABLE 4-27. Annual Wasted Fuel Due to Congestion
TABLE 4-28. Wasted Fuel per Eligible Driver
The Texas Transportation Institute's (TTI) Urban Roadway Congestion Annual
Report provided figures for tables 4-27 and 4-28. TTI relies on data from
the U.S. Department of Transportation, Federal Highway Administration, Highway
Performance Monitoring System database (HPMS). (See box 1-1 for detailed information
about the HPMS.) TTI utilizes these data as inputs for its congestion estimation
model. Detailed documentation for the TTI model and estimations can be found
at http://mobility.tamu.edu/.
The sum of fuel wasted in typical congestion (recurring delay) and incident
related delays equal the annual wasted fuel for an urban area. Recurring delay
is the product of recurring delay (annual hours in moderate, heavy, and severe
delays) and average peak period system speed divided by average fuel economy.
Incident delay hours are multiplied by the average peak period system speed
and divided by the average fuel economy to produce the amount of incident fuel
wasted.
Structure, Assumptions, and Parameters
Urban roadway congestion levels are estimated using a formula measuring traffic
density. Average daily travel volume per lane on freeways and principal arterial
streets are estimated using area wide estimates of vehicle-miles of travel and
lane miles of roadway. The resulting ratios are combined using the amount of
travel on each portion of the system (freeway and principal arterials) so that
the combined index measures conditions overall. This variable weighting factor
allows comparisons between areas such as Phoenix-where principal arterial streets
carry 50 percent of the amount of travel of freeways-and cities such as Phoenix
where the ratio is reversed. Values greater than one are indicative of undesirable
congestion levels. Readers seeking the algorithm for the congestion index should
examine http://mobility.tamu.edu/.
In previous reports, TTI assumed that 45 percent of all traffic, regardless
of the urban location, occurred in congested conditions. TTI indicated that
this presumption overestimated travel in congested periods. Its 2002 estimates
now vary by urban area anywhere from 18 to 50 percent of travel that occurs
in congestion. TTI's model structure applies to two types of roads: freeways
and principal arterial streets. The model derives estimates of vehicle traffic
per lane and traffic speed for an entire urban area. Based on variation in these
amounts, travel is then classified under 5 categories: uncongested, moderately
congested, heavily congested, severely congested, and extremely congested (a
new category in 1999). The threshold between uncongested and congested was changed
in 1999. Previous editions classified congested travel when area wide traffic
levels reached 14,000 vehicles per lane per day on highways and 5,500 vehicles
per lane per day on principal arterial streets. For the current edition these
values are 15,500 and 5,500 vehicles per lane per day respectively. Previous
years values have been re-estimated based on these new assumptions. Readers
should refer to the TTI website for more detailed information on its estimation
procedures http://mobility.tamu.edu/.
TTI reviews and adjusts the data used in its model, including statewide average
fuel cost estimates (published by the American Automobile Association) and the
number of eligible drivers for each urban area (taken from the Statistical Abstract
of the United States, published by the U.S. Department of Commerce, Bureau of
the Census).The model has some limitations because it does not include local
variations (such as bottlenecks, local travel patterns, or transportation improvements)
that affect travel times. TTI documentation does not provide information on
peer-review, sensitivity analysis, or estimation errors for their model. Information
about sensitivity analysis or external reviews of the model could not be obtained
and users should interpret the data cautiously.
ENVIRONMENT
TABLE 4-38. Estimated National Average Vehicle
Emissions Rates by Vehicle Type and Fuel
TABLE 4-39. National Average Vehicle Emissions
Rates by Vehicle Type Using Reformulated Gasoline
The U.S. Environmental Protection Agency uses its Mobile Source Emissions Factor
Model (MOBILE) to generate average emissions factors for each vehicle and fuel
type. The methods used in the model are theoretically sound, the assumptions
are reasonable, but the data vary in quality, and no formal analysis of the
accuracy of these estimates has been performed. Emissions rate estimates for
light-duty vehicles are considered more reliable than those for heavy-duty vehicles
because in-use emissions tests are performed on a sample of vehicles each year.
Deterioration for heavy-duty vehicles in the national fleet are based only on
manufacturer's engine deterioration tests. In addition, because reformulated
fuels (table 4-39) are newer than other gasoline fuels (table 4-38), in use
emissions test data for reformulated fuels are not as extensive.
The estimates in the tables represent average emissions rates taking into account
the characteristics of the nation's fleet, including vehicle type and age, and
fuel used. The model also assumes Federal Test Procedure conditions. The model
does not take into account actual travel distributions across different highway
types with their associated average speeds and operating mode fractions, nor
do they consider ambient local temperatures. However, fleet composition and
deterioration because of age are considered. Thus, these rates illustrate only
trends due to vehicle emissions control improvements and their increasing use
in the national fleet and should not be used for other purposes.
TABLES 4-40, 4-41, 4-42, 4-43, 4-44, 4-45 and
4-46. Estimates of National Emissions of Carbon Monoxide, Nitrogen Oxides, Volatile
Organic Compounds, Particular Matter, Sulfur Dioxide, and Lead
Emissions by sector and source are estimated using various models and calculation
techniques and are based on a number of assumptions and on data that vary in
precision and reliability. The methods used are theoretically sound, the assumptions
are reasonable, but the data vary in quality, and no formal analysis of the
accuracy of these estimates has been performed.
Carbon Monoxide (CO), Nitrogen Oxides (NOx), and
Volatile Organic Compounds (VOCs)
Highway vehicle emissions of CO, NOx, and VOC are generated by the U.S. Environmental
Protection Agency's (EPA's) Mobile Source Emissions Factor Model (MOBILE), which
uses per-mile vehicle emissions factors and vehicle travel (vehicle-miles) to
calculate county-level emissions. Emissions rates are then adjusted based on
fuel characteristics, vehicle fleet composition, emissions control measures,
average vehicle speed, and other factors that can affect emissions. (Emissions
rates used in MOBILE are based on vehicle certification tests, emissions standards,
and in-use vehicle tests and are updated approximately every three years.) The
U.S. Department of Transportation, Federal Highway Administration's Highway
Performance Monitoring System is the source of vehicle travel estimates used
in the model. Although the methodology for this survey data is sound and well
documented, analyses have shown that individual states vary in how rigorously
they follow the established sampling guidelines.
The non-highway vehicle emissions are calculated annually by running EPA's
NONROAD model for all categories except aircraft, commercial marine vessels,
and railroads, which are calculated via emission factors and relevant activity
data. Inputs to the NONROAD model include average temperatures, Reid vapor pressure,
fuel usage programs and controls.
Particulate Matter Under 10 Microns (PM-10) and
2.5 Microns (PM-2.5) in Size
Highway vehicle emissions are estimated using the U.S. Environments Protection
Agency's PART model, which estimates emissions factors for exhaust emissions
and brake and tire wear by vehicle type. Exhaust emissions factors are based
on certification tests, while brake wear (per vehicle) and tire wear (per tire)
are assumed values, which are constant over all years. Per-mile emissions factors
are multiplied by vehicle travel (vehicle-miles) and adjusted to account for
other factors that effect exhaust emissions (e.g., fuel composition, weather,
etc.). The U.S. Department of Transportation, Federal Highway Administration's
Highway Performance Monitoring System is the source of vehicle-miles of travel
(VMT) estimates used in the model. While the methodology for this survey data
is sound and well documented, analyses have shown that individual states vary
in how rigorously they follow the established sampling guidelines.
Fugitive dust estimates for paved and unpaved roads are calculated by multiplying
VMT on each type of road by emissions factors for each vehicle type and road
type.
The non-highway vehicle emissions are calculated annually by running EPA's
NONROAD model for all categories except aircraft, commercial marine vessels,
and railroads, which are calculated via emission factors and relevant activity
data. Inputs to the NONROAD model include average temperatures, Reid vapor pressure,
fuel usage programs and controls.
Sulfur Dioxide (SO2)
Highway vehicle SO2 emissions are estimated by multiplying vehicle travel (for
each vehicle type and highway type) by an emissions factor reflecting each vehicle
type and highway type. Highway SO2 emissions factors are based on vehicle type
and model year, sulfur content of fuel by type and year, fuel density by fuel
type, and vehicle fuel efficiency by type and model year.
In general, estimates for non-highway vehicles are calculated based on fuel
consumption and sulfur content of fuel, though other factors may be considered.
Lead
In general, lead emissions are estimated by multiplying an activity level
by an emissions factor that represents the rate at which lead is emitted for
the given source category. This estimate is then adjusted by a factor that represents
the assumed effectiveness of control technologies. For lead released during
combustion, a top-down approach is used to share national estimates of fuel
consumption by fuel type to each consumption category (e.g., motor fuel, electric
utility, etc.) and, subsequently, each source (e.g., passenger cars, light-duty
trucks, etc.).
TABLE 4-47. Air Pollution Trends in Selected Metropolitan
Statistical Areas (MSAs)
TABLE 4-48. Areas in Nonattainment of National Ambient Air Quality Standards
for Criteria Pollutants
The U.S. Environmental Protection Agency measures concentrations of pollutants
in the ambient air at its air quality monitoring sites, which are operated by
state and local agencies. These sites conform to uniform criteria for monitor
siting, instrumentation, and quality assurance, and each site is weighted equally
in calculating the composite average trend statistics. Furthermore, trend sites
must have complete data for 8 of the 10 years in the trend time period to be
included. However, monitoring devices are placed in areas most likely to observe
significant concentrations of air pollutants rather than a random sampling of
sites throughout the nation.
TABLE 4-49. U.S. Carbon Dioxide Emissions from
Energy Use by Sector
The combustion of fossil fuels, such as coal, petroleum, and natural gas, is
the principal anthropogenic (human caused) source of carbon dioxide (CO2) emissions.
Since fossil fuels are typically 75 percent to 90 percent carbon by weight,
emissions from the combustion of these fuels can be easily measured in carbon
units, as is shown in the table.
CO2 emissions data are derived from estimates. The U.S. Department of Energy,
Energy Information Administration (EIA), estimates CO2emissions by multiplying
energy consumption for each fuel type by its carbon emissions coefficient, then
subtracting carbon that is sequestered by nonfuel use of fossil fuels. Carbon
emissions coefficients are values used for scaling emissions to specific activities
(e.g., pounds of CO2emitted per barrel of oil consumed).
Emissions estimates are based on energy consumption data collected and published
by EIA Several small adjustments are made to its energy consumption data to
eliminate double counting or miscounting of emissions. For example, EIA subtracts
the carbon in ethanol from transportation gasoline consumption because of its
biological origin.
Emissions coefficients are based on the density, carbon content, and heat content
of petroleum products. For many fuels, except liquefied petroleum gas (LPG),
jet fuel, and crude oil, EIA assumed coefficients to be constant over time.
For LPG, jet fuel, and crude oil, EIA annualized carbon emissions coefficients
to reflect changes in chemical composition or product mix.
Since the combustion of fossil fuels is a major producer of CO2emissions, sources
of uncertainty are related to: 1) volumes of fuel consumed; 2) characteristics
of fuel consumed; 3) emissions coefficients; and 4) coverage. EIA notes that
volumetric fuel data are fairly reliable in the 3 percent to 5 percent range
of uncertainty. The density and energy content of fuels are usually estimated.
According to EIA, the reliability of these estimates vary. For example, estimates
of the energy content of natural gas are reliable to 0.5 percent, while estimates
for coal and petroleum products are lower because they are more heterogeneous
fuels. The reliability of emissions coefficients depends on whether the characteristics
of a fuel are difficult to measure accurately. Finally, uncertainties may result
because data may be excluded or unknown sources of emissions not included.
EIA's estimation methods, emissions coefficients, and the reliability of emissions
estimates are discussed in detail in U.S. Department of Energy, Energy Information
Administration, Emissions of Greenhouse Gases in the United States, 1998
available on: www.eia.doe.gov/oiaf/1605/ggrpt/index.html.
TABLE 4-50. Petroleum Oil Spills Impacting U.S.
Waterways
The U. S. Coast Guard's (USCG) Marine Safety Information System (MSIS) is the
source of these data. It includes data on all oil spills impacting U.S. navigable
waters and the Coastal Zone. The USCG learns of spills through direct observation,
reports from responsible parties and third parties. Responsible parties are
required by law to report spills to the National Response Center (NRC).Reports
may be made to the USCG or Environmental Protection Agency pre-designated On
Scene Coordinator for the geographic area where the discharge occurs if direct
reporting to the NRC is not practicable. There is no standard format for these
reports, but responsible personnel face significant penalties for failing to
do so. Most reports are made by telephone, and USCG personnel complete investigations
based on the information provided. The type and extent of an investigation conducted
varies depending on the type and quantity of the material spilled. Each investigation
will determine as closely as possible source of the pollutant, the quantity
of the material spilled, the cause of the accident, as well as whether there
is evidence that any failure of material (either physical or design) was involved
or contributed to the incident. These are so financial responsibility may be
properly assigned for the incidents, as well as proper recommendations for the
prevention of the recurrence of similar incidents may be made.
Some spills may not be entered into MSIS because they are either not reported
to or discovered by the USCG. The probability of a spill not being reported
is inversely proportional to its size. Large spills impact a large area and
a large number of people, resulting in numerous reports of such spills. Small
spills are less likely to be reported, particularly if they occur at night or
in remote areas where persons other than the responsible party are unlikely
to detect them. Responsible parties are required by law to report spills and
face penalties for failing to do so, providing a strong incentive to report
spills that might be detected by others. Experience with harbor patrols shows
that the number of spills increases as the frequency of patrols increases. However,
the volume of material spilled does not increase significantly, indicating that
the spills discovered through increased harbor patrols generally involved very
small quantities.
Data Collection
From 1973 to 1985, data were collected on forms completed by the investigator
and later entered into the Pollution Incident Reporting System (PIRS) by data
entry clerks at USCG headquarters. Since 1985, data have been entered directly
into MSIS by the investigator. From 1985 to 1991, data were entered into a specific
electronic form that captured information on the spilled substance and pollution
response actions. Since 1995, a growing number of reports of pollution incidents
of 100 gallons or less of oil have been captured on a Notice of Violation ticket
form, which are then entered into MSIS.
The information shown in this table comes from the USCG Spill Compendium, which
contains spill data from the applications described above. The Compendium contains
summary data from 1969 through 2000 and is intended to provide general information
to the public, the maritime industry and other interested persons about spills
in and around U.S. waterways. For more information about spill data, please
refer to the USCG Internet site at http://www.uscg.mil/hq/g-m/nmc/response/stats/aa.htm
Nonsampling Errors
According to the USCG, nonsampling errors, such as nonreporting and mistakes
made in data collection and entry, should not have a major impact on most interpretations
of the data, but the impact will vary depending on the data used. The error
rate for volume spilled is estimated to be less than 5 percent because larger
spills, which account for most of the volume of oil spilled, are thoroughly
reviewed at several levels. The error rate for the number of spills is difficult
to estimate primarily due to low reporting rates for small spills. Most of the
error in spill counts involves spills of less than 100 gallons.
TABLE 4-51. Leaking Underground Storage Tank Releases
and Cleanups
A national inventory of reported spills and corrective actions taken for leaking
underground storage tanks is compiled biannually based on state counts of leaking
tanks reported by owners as required by the Resource Conservation and Recovery
Act of 1976.1 These data may be affected by general
accounting errors, some of which have changed semiannual counts by as many as
2,000 actions.
TABLE 4-52. Highway Noise Barrier Construction
State highway agencies (SHAs) provide data on highway noise barrier construction,
extent, and costs to the U.S. Department of Transportation, Federal Highway
Administration. Individual SHA definitions of barriers and costs may differ.
This could lead to nonuniformity and/or anomalies among state data, which will
in turn affect national totals.
TABLE 4-53. Number of People Residing in High-Noise
Areas Around U.S. Airports
The number of the people exposed to aircraft noise around airports is estimated
by computer modeling rather than by actual measurements. The U.S. Department
of Transportation (USDOT), Federal Aviation Administration's (FAA's) Integrated
Noise Model (INM) has been the primary tool for assessing aircraft noise around
airports for nearly 30 years. This model uses information on aircraft mix, average
daily operations, flight tracks, and runway distribution to generate and plot
contours of Day Night Sound Level (DNL).With the addition of a digitized population
census database, the model can estimate the number of residents exposed to noise
levels of 65 decibels (db) DNL.
The U.S. Environmental Protection Agency (EPA) produced the first estimate
of airport noise exposure in 1975.It reported that 7 million residents were
exposed to significant levels of aircraft noise in 1978.This number became the
"anchor point" for all future estimates of the nationwide noise impacts. In
1980, FAA developed another methodology for estimating the change in the number
of people impacted by noise (from the 1975 anchor value) as a function of changes
in both the national fleet and in the FAA's Terminal Area Forecast (TAF). In
1990, the FAA created an improved method of estimating the change in number
of people impacted (relative to the 1980 estimates).
In 1993, the FAA began using its newly developed Nationwide Airport Noise Impact
Model (NANIM) to estimate the impact of airplane noise on residential communities
surrounding U.S. airports that support jet operations. FAA uses this model to
determine the relative changes in number of people and land area exposed to
65 db DNL as a result of changes in nationwide aircraft fleet mix and operations.
NANIM uses data on air traffic patterns found in the Official Airline Guide
(OAG), air traffic growth projections found in FAA's TAF, population figures
from the U.S. Census Bureau, and information on noise contour areas for the
top 250 U.S. civil airports with jet operations.
The methodology used in NANIM has been peer reviewed and approved. However,
a formal evaluation of the model's accuracy has not been conducted. Some data
used in NANIM are updated manually, thus the possibility of data entry errors
does exist. Entries are reviewed and then corrected as appropriate. The aircraft
mix and operations files from FAA's TAF and OAG are updated automatically. Changes
to either of the sources could introduce errors. For example, it was recently
discovered that OAG redefined some aircraft codes and altered some data fields
in its database. These changes make it impossible for the NANIM utility program
to accurately read the current OAG database. A rewrite of the source code is
necessary to eliminate this error. Also, since airport authorities are not required
to produce noise exposure maps and reports unless they intend to apply for Federal
grants, 14 of the 50 busiest commercial airports, including JFK and LaGuardia,
have not produced (for public consumption) noise exposure maps in several years.
In the absence of actual data, the NANIM database contains approximations of
the noise contours areas based on airports of similar size and similar operation.
Without actual airport data, it is impossible to quantify the error introduced
by the approximation.
The number of people exposed to aircraft noise for 1998 through 2001 was estimated
by the FAA's latest version of its MAGENTA model. This new, more accurate model
is based on 2000 census data and uses input data on aircraft and operations
specific to U.S. airports. This revised model also uses the FAA Terminal Forecast
(TAF), which provides information on how operations will increase on an airport
specific basis. Updated monthly, the TAF allows a more accurate forecast of
U.S. operations.
TABLE 4-54. Motor Vehicles Scrapped
The Polk Company's Vehicles in Operation database is the source of these data.
This database is a census of vehicles that are currently registered in all states
within the United States. It is based on information from state department of
motor vehicles. Polk updates the database quarterly (March, June, September,
and December).
Scrapped vehicles are those that Polk removes from its database when: 1) States
indicate registered vehicles have suffered major damage (such as a flood or
accident), or 2) No renewal (reregistration) notice is received by Polk within
a state's allotted time (normally one year). In the latter case, if a vehicle
is subsequently reregistered, it is returned to the database. The Polk data
on motor vehicles is broken down into passenger cars and trucks, and this identification
comes with the registration data from the DMV.
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of Petroleum Supply Data. Tammy G. Heppner and Carol L. French, eds.Washington,
DC.
U.S. Department of Energy, Energy Information Administration. 1990. Energy
Consumption by End-Use Sector, A Comparison of Measures by Consumption and Supply
Surveys, DOE/EIA-0533.Washington, DC.
U.S. Environmental Protection Agency, Office of Mobile Sources. 1998.MOBILE5
Information Sheet #7: NOx Benefits of Reformulated Gasoline Using MOBILE5a.
Ann Arbor, MI. September 30.
U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards.1998.National
Air Pollutant Emission Trends, Procedure Document, 1900-1996. EPA-454/R-98-008.Research
Triangle Park, NC.May.
U.S. Environmental Protection Agency, Office of Mobile Sources. 1996.Memorandum
on Release of MOBILE5b.(Revised Chapter 2 for the Users Guide to MOBILE5).October
11.
U.S. Environmental Protection Agency, Office of Air Quality and Standards,
Emission Factor and Inventory Group.1995.Compilation of Air Pollutant Emission
Factors AP-42, Volume II: Mobile Sources. Appendix H. Fifth ed.June 30.
U.S. Environmental Protection Agency, Office of Mobile Sources (OMS). 1995.
Draft User's Guide to PART5: A Program for Calculating Particle Emissions
from Motor Vehicles, EPA-AA-AQAB-94-2.Ann Arbor, MI.February.
U.S. EPA, Office of Mobile Sources.1994. Users Guide to MOBILE5 (Mobile
Source Emission Factor Model),EPA-AA-TEB-94-01.Ann Arbor, MI.May.
U.S. Environmental Protection Agency, Office of Air and Radiation. 1992. Procedures
for Emission Inventory Preparation, Volume IV: Mobile Sources, EPA-450/4-81-026d
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1 Public Law 94-580, 90 Stat. 2795 (October 21, 1976).
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